Abstract: Aims The broad-leaved Korean pine mixed forest, as the zonal climax vegetation in eastern Northeast China, has been severely disturbed by long-term human activities. As a result, most primary forests have degraded into secondary poplar-birch forests. However, relevant systematic comparative studies between these two forest types remain insufficient, limiting our understanding of the natural recovery process of the broad-leaved Korean pine mixed forest. Methods Based on a 24-ha permanent forest dynamics plot in Changbai Mountain, we employed the paired correlation function g(r) and the heterogeneous Poisson null model to compare the spatial distribution and interspecific association patterns of tree species between the northern secondary poplar-birch forest (early successional stage, 15.6 ha) and the southern broad-leaved Korean pine mixed forest (late successional stage, 8.4 ha) within the plot. Important findings (1) Most tree species in both forest types exhibited scale-dependent spatial patterns, showing aggregated distribution at small scales (0-10 m) and random distribution at larger scales (>20 m). Clustering intensity was generally higher for small and medium-sized trees (DBH < 30 cm) than for large trees (DBH ≥ 30 cm). In the secondary poplar-birch forest, large trees were mostly randomly distributed, whereas in the broad leaved Korean pine forest, large trees remained aggregated at small scales (0-10 m). (2) Interspecific associations among tree species were predominantly random in both forest types. Large trees exhibited a higher proportion of negative interspecific associations than small trees. While large trees showed both facilitative and inhibitory effects on small sized individuals, they mainly exhibited competitive suppression on medium sized individuals. (3) As a key foundation species, Pinus koraiensis exhibited aggregated distribution patterns in both forest types. However, its aggregation intensity was lower in the broad-leaved Korean pine mixed forest, where it exhibited negative spatial associations with pioneer species such as Betula platyphylla and Populus davidiana. In contrast, small P. koraiensis trees in the secondary poplar–birch forest displayed significant positive associations with these pioneers. These findings indicate that pioneer species facilitate the establishment of small P. koraiensis trees during early succession but become progressively suppressed and are eventually excluded as forest succession proceeds. Overall, the species distribution and interspecific association patterns were broadly similar between the two forest types, whereas pronounced differences were observed for key foundation species, such as P. koraiensis. These results enhance our understanding of the natural recovery process of the broad-leaved Korean pine mixed forest and provide valuable insights for forest management and restoration of temperate forests of Northeast China.

Key words: spatial distribution, spatial association, spatial point pattern analysis, broad-leaved Korean pine forest, secondary poplar-birch forest